The Bell Rock, as appears by the best charts of the coast, is situated at the mouth of the Firth of Forth, in west longitude 2° 22´, and north latitude 56° 29´. It lies nearly fifteen miles from the Island of May, in a north-eastern direction per compass, and twelve miles south-west from the Red-head in Angusshire, which it resembles, being a free-stone of a reddish colour, though of a much harder body, and closer grit. Besides its natural asperities, the surface in general is thickly coated with sea-weed, and, on the higher parts, the barnacle, white buckie or whelk, and limpets, abound, and altogether it presents a very rugged appearance, owing to the sloping of the strata from south, where highest, to north, at an angle of about 30 degrees. The material part of the rock, which lies north-east and south-west, measures, on an average, about 300 feet in length, and 240 feet in breadth. The highest part above the surface of the sea, does not exceed seven feet at low-water of spring-tides; which part, at high-water of same tides, is from nine to ten feet under water. The reporter also found, that the medium height of the foundation of any building erected upon it, will not exceed two or three feet above the surface of the sea at low-water of spring-tides. The above dimensions may be termed the material part of the rock; but, south-west of this, there runs a reef or shoal, of considerable extent, which is only visible in very low tides.
The short time which the Bell Rock is seen above water, and the irregularity of the soundings in its vicinity, are the cause of many wrecks upon it. Indeed, after the water has flowed, in ordinary tides, but a very short time, the most skilful mariner cannot point out its place, without its proper meaths or land-marks in sight, which lie from twelve to twenty miles distant. Under these circumstances, the Bell Rock will be found more dangerous to vessels coming near it, than perhaps any of those reefs upon which Light-houses have as yet been erected.
The Edystone Rock, for example, is about eleven miles from land, situate at the entrance of Plymouth Sound. Before the rock was reduced for the foundation of the Light-house, it was about three feet above high-water of spring-tides. The Longships Rock, situate three miles off the Lands-End, is about forty feet above high-water mark, though barely large enough for the foundation of the Light-house. The Smalls lie fourteen miles off St David’s Head; and the rock on which the light-house is built, is about five feet above high-water of spring-tides. The South Rock, lying three miles off the land, between Loch Strangford and Donaghadee, is about four feet under the surface at high-water of spring-tides. The Tour de Corduan, upon the coast of France, is built upon a sunken rock at the entrance of the Garonne, and is said to be about eight feet under the surface of the sea at high-water of spring-tides. And, lastly, the Bell Rock, the subject of this report, lying upwards of eleven miles from land, is from nine to ten feet under water, as before stated.
Ever since the reporter had an opportunity to know the danger and inconvenience that must attend the navigation of the Firth of Forth, while the Bell Rock remains without some signal upon it, to forewarn seamen, he has been much employed in considering what kind of building would be most applicable to its situation; and he has, therefore, endeavoured to obtain as much information as possible about works of this kind. The first light-house erected upon an insulated rock on the coast of Great Britain or Ireland, appears to have been that of the Edystone, which was begun in 1696, and was scarcely finished, when a dreadful storm carried it completely away. This erection was constructed of timber, and was designed and executed by Mr William Winstanly, who, with his artificers and the light-keepers, unfortunately perished in its ruins. The next light-house that was built upon the Edystone Rocks, consisting partly of stone and partly of wood, it was finished in 1709, and was the work of Mr John Rudyard, who, carefully avoiding the errors of his predecessor, lopped off all superfluous ornaments, and produced a plain building; which, after withstanding the fury of the waves for forty-nine years, had the misfortune to be destroyed by fire. The present Edystone Light-house was begun in 1756, and finished in 1759. It has now stood forty-four years, a memorial of the ingenuity and indefatigable labours of Mr John Smeaton, who, guarding against the defects of the two former buildings, constructed the whole of stone; the blocks of the solid part are curiously dove-tailed into each other; and every thing unnecessarily tending to give resistance to the water is carefully avoided, while the whole is completely fire-proof. The next light-house erected upon a situation of this kind, was the Smalls, which is placed upon eight beams of oak, arranged round a centre one. The latest light-house built on an insulated situation, is that upon the South Rock on the coast of Ireland. The reporter made three successive journeys to this light-house, during its progress: First in 1796, when it was only 12 feet in height; again in 1797, when it was nearly finished; and a third time in the month of August 1800. This light-house is built of granite, quarried in the mountains of Morne. The method of dove-tailing or joggling the stones, and attaching the courses to each other, is different from that of the Edystone; throughout the solid part of the masonry, and eighteen inches within the circumference of the building, six great bars of malleable iron are carried up, each four inches square; and upon the top of every alternate course, a circular plate of iron is let into the stone, and fixed by spear-bolts to the upright bars. The building is of a conical figure, and was built in the course of three years from a design by Mr John Rodgers of Dublin.
Before being properly certified as to the possibility of getting a foundation for a building of any kind upon the Bell Rock, the reporter thought of a Floating-light, like those moored off the Dudgeon-shoal, and other sand-banks on the coast of England. But the foulness of the ground about the Bell Rock, the great depth of water near it, together with the unsteadiness of a light of this description,—and above all, the perplexing uncertainty which must ever attend such a light in a storm, cannot fail to unhinge the confidence of the mariner, and thereby prevent him from making free with his course; and when, from an error in it, or in the distance run, he is disappointed in seeing the light, wrong conclusions are apt to be formed: he supposes that the Floating-light has drifted, and by changing his course, perhaps turns upon the very point of danger. These were considerations from which much relief was felt, upon learning that the rock was large enough to form the foundation of a permanent building; but, till the moment he landed upon it, he was uncertain if a building of stone was applicable; and foreseeing the difficulties which would be avoided, if, instead of carrying up the lower part solid, it could be formed of pillars, after the manner of the Smalls Light-house; reflecting also upon that elegant and useful application lately made of cast-iron, in the construction of bridges, choice was made of this metal, in his first model for the Bell Rock, as being more substantial than timber, and also less liable to corrosion from the action of the atmosphere than malleable-iron. This light-house (see [Plate VII.]), was to consist of six hollow tubes or pillars, built each to the height of ninety feet, measuring two feet in diameter at the base, and diminishing to six inches at the top, ranged round a common centre so as to form a diameter of thirty-five feet at the base, and eight feet at the top, immediately under the light-room. The pillars were to be cast in lengths or pieces of ten feet each; and at every joint horizontal bars were made to grasp the pillars, and the whole was also connected diagonally with various cross braces. Under the light-room, the building was to be laid out into four heights of apartments for the light-keepers and stores, formed within the range of the pillars, which occupying 45 feet of their height, the part below being of similar height, was left free for the passage of the sea, thus presenting the least possible resistance to the waves. These apartments were to be formed and covered in with strong copper, which, to prevent its acting upon the iron, was to be coated with tin. The lower part, or floor nearest to the sea, was to form an inverted cone, presenting a surface calculated to disperse the seas which might strike against it. In order still more to increase the common base, and strengthen this fabric, Professor Robison advised that a diagonal bar should be attached to the exterior side of each of the pillars.
In this first design, provision was made chiefly against the impulse of the sea, without taking into account the possibility of a vessel or wreck getting near it; but he found, after landing upon the rock, that it was possible for a vessel at high-water to come, without interruption, against the pillars. To guard against misfortune from this quarter, the reporter first thought of defending the pillars in various ways, particularly by throwing a kind of Chevaux de Frise round them, with beams of oak. He, however, found it difficult to suppose any set of pillars of adequate strength to resist the force of a loaded vessel, violently agitated in a winter storm, which must render the pillar-formed construction very uncertain, even after every precaution should be taken to guard against such accidents. Nor ought the danger to which such a mass of metal, constantly exposed to the effects of the marine-acid, to be wholly overlooked, in giving a preference to a circular building of stone, which being a compact figure of solid matter, would resist any force that might be brought against it. The reporter has estimated the Pillar-formed Light-house at L. 15,000; and, although that for the Tower of masonry amounts to L. 42,636, 8s., yet, as it is treading a beaten path, which leads to certainty, it is surely to be preferred in a work of this kind: the foundation-course of stone must be more tedious than that of so many pillars, yet, in this there is nothing impracticable; and when the difficulties of the first courses are surmounted, the superiority of a fabric of stone over one of iron will readily be admitted.
In the model for a building of stone, made since the reporter first landed upon the Bell Rock, he has retained nearly the same elevation as that of the Edystone Light-house, which presents less resistance, and preserves a greater base than perhaps any other figure that could have been thought of. In this design he has also followed Mr Smeaton in the use of oak-trenails to keep the stones in their places, while the work is in progress; but has differed in the mode of diminishing the interior-walls, as the building rises in height. Instead, also, of Mr Smeaton’s plan of dove-tailing the stones, and connecting the floors, various other modes are resorted to, for effecting this perpendicularly as well as laterally, with the view of introducing larger materials, and keeping the stones in a more entire state. One of these is by an iron-bat, which is inserted into the joints of the lower courses, while the void or upper courses are to be indented, or let perpendicularly into one another. Upon inspection of the models and drawings of this design, it will perhaps be found to render the construction more simple, to divide the strength of the walls more equally, and, upon the whole, to give that stability which the situation of the Bell Rock seems so peculiarly to require. (See [Plate VII.])
Upon comparing the pillar-formed Light-house, with the circular tower of masonry, it is matter of surprise that ever the Smalls Light-house should have been erected upon that plan, unless it were to avoid the additional expence of a stone building. There is, however, one circumstance which materially favours the pillar-formed construction at the Smalls, the want of which becomes a principal objection to its application at the Bell Rock; namely, that the Smalls Rock being five feet above high-water of spring-tides, the pillars are more obviously defended from injury in the event of a vessel or wreck coming against them, and also from the violence of the sea, whereas the Bell Rock, at certain periods of the tide, is from nine to ten feet under water.
When Mr John Rennie, civil engineer, obligingly favoured the reporter by examining his models, he gave a decided preference to the structure of stone, as did Professors Robison and Playfair. And Captain Huddart also, upon seeing the pillar-formed model, mentioned that the Trinity-House did not approve of iron pillars which, in the instance of the Smalls, were considered not so proper as beams of oak. The chief motives which induced the reporter to model a light-house upon the plan of the Smalls, were the uncertainty of procuring a foundation for a stone building; the small resistance which the pillars present to the force of the waves, and the first cost being very considerably less. But although this is true, with regard to the resistance, it must also be remembered, that the pillars come prodigiously short of the weight of a tower of masonry, of the dimensions of the one modelled, containing upwards of 2000 tons; whereas the iron pillars, even in their most improved state, do not exceed 200 tons. When, therefore, the stone light-house is compared with the iron one, all idea of the greater resistance of the former is lost in its solid contents, and in the uniformity of its figure.
In alluding to the great utility of an erection on the Bell Rock, it may, in general, be observed, that it is in the same degree of latitude with the Town of Holstebro in Denmark, and that the Naze of Norway, or entrance to the Baltic, lies north of Holstebro 1° 30´. It therefore follows, that all vessels bound to the Baltic, from, any port south of the River Tweed, must cross the latitude of the Bell Rock, while the degree of east or west longitude, in which such vessels pass, must depend upon the direction of the winds and other circumstances. In order to avoid the enemy in the time of war, it is common for shipping in this track, first to make the land about Buchanness in Aberdeenshire, and from thence take their departure either over seas, or along shore to their respective ports. With regard to ships bound for Archangel and Greenland, they, at all times, make the Islands of Shetland, and from thence take their departure. If, therefore, lines be drawn from Buchanness and Girdleness in Aberdeenshire, to Flamborough Head in Yorkshire, and the mouth of the Tyne in Northumberland, the Bell Rock will only be found to lie from six to ten leagues distant from these courses or lines. So that vessels crossing the mouth of the Firth of Forth, from Buchanness to the Humber and Thames, &c., may not only come in sight of a light upon this rock, but be materially benefited by it, according to the state of the weather, while those upon the course of the nearest line bound for Newcastle and Sunderland, &c. must, in every voyage which carries them north of the Tweed, be essentially served by a light upon the Bell Rock.